One thing to bear in mind is that documentation serves two different audiences.

One audience is the people who will use your code. For them, every external method should be properly documented (sure, use a tool for this). And make sure it's good enough that (barring debugging situations, because you wrote perfect code) your "users" never have to look inside your code. (If I think about this in C++, I think you should be able to look at a properly commented header and never read the code)

And then there's the poor slob who's going to come in and debug/fix your code some day. He may not need to have every method doc'd but he damn sure needs to know what's tricky, what's interesting, where the gotchas are, etc.